The invention relates to the art of operating oil fields by the shaft method, and, more particularly, to a method for thermoshaft oil production.
The present invention may be most advantageously used in operating oil fields with highly viscous oils and mobile (fluid) bitumens.
The invention may also be used for operating low-pressure oil fields.
At present, such oil fields cannot be operated by conventional methods, such as using holes drilled from the surface since the oil yield is very low.
For operating oil fields with highly viscous oils or mobile bitumens, a shaft oil production method was used heretofore which involved production without lifting the oil-saturated rock up to the surface.
This thermoshaft of oil production comprises the provision of a system of mining openings 10-30 m above the roof of the production oil-bearing bed. Then the mining field is divided into several levels. Longitudinal field drifts with drilling chambers are made between the levels. According to a selected pattern, inclined and vertical holes are drilled into the production bed at a depth of about 40-70 m from the drilling chambers and are spaced at 40-60 m from one another. The hole depth depends on the thickness of the oil-bearing bed.
The distance between the hole bottoms, the number of holes and the pattern of arrangement of mining openings of this oil production method may vary.
The hole bottoms are uniformly distributed over the bed foot with the spacing of the hole bottoms being from 12 to 25 m.
The hole construction involves the provision of a four-inch casing string which is grounded at the mouth of the hole. The hole bottom is of the open type. The hole mouth is provided with elbow bends and fittings.
After the drilling, the holes are operated, first by the gusher method, and then by the airlift method.
Oil is collected and transported in an open-type system. The oil from the holes is fed into channels of the mining openings and is conveyed therealong by water to oil traps (hydraulic transportation). Oil with water is pumped from the traps into central underground oil collectors. Then, after primary handling and heating, the oil is pumped into oil storage tanks.
The above-described method enables, depending on the geological and physical characteristics of the production oilbearing bed and the fluids saturating it, the use of an optimal arrangement of the holes for operating oil fields so as to ensure an improved oil yield with low drilling costs.
This method also offers wide possibilities of using structural analysis for drilling directional holes into the zones of tectonic dislocations, non-operated zones and zones with elevated permeability of the bed.
In addition, the employment of this method simplifies production methods in drilling holes, oil production and transportation and enables elimination of the influence of climatic conditions on regularity of oil production operations.
However, inspite of a therefold improvement of oil yield of the bed, absolute oil yield is as low as about 6% when using this method as compared to the operation of holes drilled from the surface.
Furthermore, the use of this method results in the need for performing a large number of effort-consuming mining and drilling operations in empty oil-less rocks.
It should be also noted that a large scatter and an enormous number of operating holes considerably complicate the performance of extensive geological and technical measures associated with successful operation of the holes.
The above-described difficulties result in the need for the employment of oil production methods involving physical and chemical action on the production oil-bearing bed and the fluid saturating the same.
Known also in the prior art is a thermoshaft oil production method using a steam action on the production oil-bearing bed.
This method involves the provision of a combination using a steam action on the production oil-bearing bed.
This method involves the provision of a combination of mining openings above the oil-bearing bed.
Vertical and inclined holes are drilled from said mining openings. A part of the holes are used for feeding a heating medium (steam) into the production oil-bearing bed (injection holes), and the other holes are used for recovery of oil from the bed (production holes). It should be noted that all operations associated with feeding steam into the bed are performed using the common practice of feeding a heating medium through conventional holes drilled from the surface.
This method provides positive displacement of the oil with the steam from the bottoms of the injection holes to the bottoms of the production holes.
Accordingly, the holes are operated by the airlift method.
With small production volume, this method intensifies the process of oil production, reduces steam consumption for recovery of one ton of oil and reduces the number of concurrently operated injection holes as compared to similar known oil production methods.
However, with greater production volumes in recovering oil from production holes operated by the airlift method, sand plugs are frequently formed, and the holes are plugged with sand effluent from the production bed.
In addition, extra expenses are required for the provision of hole mouths with check fittings and the installation of conduits in the holes for the airlift operation, as well as an additional air supply for lifting fluid from the holes.
Apart from that, as a result of the combination of steam injection and oil production operations within the limits of the same mining openings, labor conditions and safety are impaired.
When steam injection pressure is increased above 5-6 kg/cm.sup.2, steam may break through the cracks into overburden mining openings, and avalanches may also occur in the mining openings.
Continuous steam injection cannot be performed due to the small spacing between the holes.
Rest periods in during operation of the injection and production holes result in the formation of sand plugs, complications in the operation of the holes, difficulties encountered in the airlift hot oil production and, as a result of all this, a low oil yield of the production oil-bearing bed, heavy labor conditions and bad safety in the mine.